Switch device for pressure cylinders



. L. G. TRIMMER SWITCH DEVICE FOR PRESSURE CYLINDERS u 2 sheets-sheet 1 Sept. s, 1967 Filed Oct. 23, 1955 Y SRA ky m kh* Ek RELA i SH INVENTOR. R

LEA G. TR/MME ATTORN E YS @if i.

Sept. 5, 1967 L. G. TR'IMMER Y SWITCH DEVICE FOR PRESSURE CYLINDERS 2 Sheets-Sheet 2 Filed Oct. 23, 1965 INVENTOR LEA G. TRIMMER ATTGRNE YS United States Patent O 3,340,371 SWITCH DEVICE FOR PRESSURE CYLINDERS Lea G. Trimmer, 2418 Walnut, Kansas City, M0. 64108 Filed Oct. 23, 1965, Ser. No. 503,706 4 Claims. (Cl. 200-82) ABSTRACT F THE DISCLOSURE This invention relates to pressure cylinders and, more particularly, to cylinder apparatus adapted to produce an appropriate signal when the cylinder piston has attained a predetermined position in the cylinder.

Pressure cylinders find common use in a wide variety of applications for producing a controlled axial movement. The movement is often applied in a location remote from the operator and it is desirable or necessary to provide signaling devices by which the operator can sense the position which the piston rod of the cylinder has achieved. It has been suggested to place a suitable contact actuated switch on the frame structure supporting the pressure cylinder so that the movement of the piston rod causes the piston rod or a related member to actuate the switch when a predetermined position of the rod has been attained. This has proved to be unsatisfactory in many applications because slight variations in the position of the cylinder or related members interfere with signal reliability. Further, such external mounting often exposes the signaling device to an environment of dirt, ice, grease, water, chemicals, etc. which quickly or eventually interfere with proper operation. This has led to a ban on such devices by the military and in many industrial applications.

It has been further suggested to use a pressure switch as the signaling device, which switch communicates with the feed lines to the cylinder for actuation; however, this solution has also been found unsatisfactory in many instances because the switch operates in response to variations in pressure and not necessarily in response to an actual change in position of the piston.

The principal objects of the present invention are: to provide a signaling device which is responsive only to the actual position attained by a cylinder piston; to provide such a device which is exposed to the pressure variations in the cylinder but is unresponsive thereto and independent thereof; to provide such a device which cannot fall out of adjustment due to variations in cylinder positioning on its frame support; to provide such a cylinder signaling assembly which exhibits extremely long life under rugged operating conditions; to provide a signaling device which is easily assembled with a cylinder and produces a signal only when a predetermined position has been attained by the piston in the cylinder; to provide such a device wherein the switch contacts engage in a wiping motion so as to insure electrical continuity therebetween even in the event that oil mist is introduced into vthe switch interior; to provide such an assembly wherein the switch interior is flushed by clean compressed air upon each cycle of the cylinder so as to limit corrosion problems often associated with slight leakage into hermetically sealed switches; to provide such a signaling device which is normally sealed against the ambient atmosphere but will continue to operate reliably even if a slight leak occurs in the switch body; and to provide such a cylinder assembly which is simple and inexpensive in construction and highly reliable in use.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein are set forth by way of illustration and example certain embodiments of this invention.

FIG. 1 is a partially schematic fragmentary view of an air cylinder assembly embodying this invention shown with a control circuit for use on a truck for engaging a power take-oli device.

FIG. 2 is a vertical cross-sectional view through the air cylinder assembly of FIG. l particularly showing signaling devices engaged in opposed cylinder heads.

FIG. 3 is a fragmentary cross-sectional view on an enlarged scale particularly showing a signaling device assembly just attaining contact with a cylinder piston.

FIG. 4 is a detailed view on the scale of FIG. 3 showing the stem of the signaling device separate from associated parts.

FIG. 5 is a vertical cross-sectional detailed view on the scale of FIG. 3 showing the stem retainer and switch contact arms of the signaling -device separate from associated parts.

Referring to the drawings in more detail:

The reference numeral 1 generally indicates anair cylinder assembly embodying this invention. The air cylinder assembly 1 is shown, by way of example, as part of a brake lock control system for a vehicle having a compressed air tank 2 and compressed air responsive wheel brake assemblies 3 selectively connectable to and disconnectable from the tank 2 through a solenoid valve control 4. The vehicle has a power take-0E mechanism (not shown) with an actuating member 5 adapted to selectively connect and disconnect the power take-off mechanism to the vehicle engine upon the movement thereof axially of the cylinder assembly 1 as indicated by the arrow 6.

The solenoid valve control 4 is fed compressed air through a suitable pressure source tube 7 and, upon proper actuation, directs the air through a tube 8 into the forward interior portion 9 of the air cylinder assembly 1 and simultaneously into communicating tubing 10 which Idirects air to the brake assemblies 3. The brake assemblies 3 thereby lock the vehicle wheels and the piston 11 of the cylinder assembly 1 is simultaneously moved rearwardly, pulling the piston rod 12 therewith which in turn pulls the power take-oil actuating member 5 through a connection 13 into engaged position. Thus, the brakes of the vehicle are normally locked when the power take-oilc mechanism is enga-ged.

When the solenoid valve control 4 is disengaged a spring 14 urges the valve lcontrol plunger 15 to its initial position whereupon air under pressure in the forward portion 9 and tubing 10 is allowed to exhaust to the atmosp'here. Compressed air is simultaneously introduced through tubing 16 to the rear portion 17 of the cylinder 1 causing the `actuating member 5 to move in the opposite direction, Idisengaging the power take-off while the brake assemblies 3 are disengaged for moving the vehicle. The solenoid valve control 4 is of the shifting plunger type well known in the art and further details thereof are not believed necessary to an understanding of this invention.

In using the cylinder 1 to shift the actuating member 5, it is of the utmost importance for the operator to know when the actuating member has arrived at the respective position where the power take-off is engaged or disengaged. Without this knowledge the operation of the power take-off can be dangerous to both personnel and equipment. To provide a reliable signal as to the position of the actuating member 5, signaling devices 18 and 19 are associated with the cylinder assembly 1 and integrated into the control circuit of the power take-off system as now described.

The air cylinder assembly 1 has cylinder heads 20 and 21, each having a cylindrical wall 22 with an outside surface 23 and an inside surface 24. The inside surfaces 24 form compartments 25 extending axially into the respective -cylinder heads. The cylinder heads 20 and 21 each have a circular protrusion or ridge 26 which is received in a circular groove 27 formed in the cylinder tubular wall 28 to provide line axial alignment between the interior tubular surface 29 and the respective compartments 25 of the cylinder heads 20 and 21. The grooves 27 also contain an O-ring seal 30 in sealing contact with the ends of the cylinder wall 28 and the cylinder Ihead ridges 26 to prevent air leakage between the junctions of the cylinder heads and the cylinder wall.

The piston 11 is maintained in sliding -contact with the interior surface 29 of the tubular wall 28 in the usual manner and a suitable sliding seal 31 prevents leakage due to a pressure differential between the forward portion 9 and the rear portion 17 of the cylinder assembly. The piston 11 has axially protruding end portions 32 and 33 res-pectively receivable in the cylinder head compartments 25 for trapping air therein to provide a cushion effect at the end of each forward and rearward stroke of the piston 11. The air trapped in the compartments 25 is permitted to bleed through passageways (not shown) and through adjustable restricting devices (not shown) in the usual manner so as to provide the desired degree of cushioning at the end of eac'h piston stroke.

The signaling device 18, also typical of the device 19, comprises a swit-ch housing 34 which includes a body portion 35 and a neck -portion 36. The body and neck portions 35 and 36 are integral with each other and lpreferably comprised of an easily machined non-conductive high impact strength synthetic resin such as Delron or nylon. The body portion 35 has a cylindrical side wall 37 and one end wall 38 forming a hollow interior 39 with an open end `40 opposite to the end wall 38. The neck portion 36 axially protrudes lfrom the end wall 38 and is of smaller outside diameter than the side wall 37. The neck portion 36 has external threads 41 thereon and a central bore 42 extending axially therethrough and communicating through the end wall '38 with the hollow interior 39. The central bore 42 has a narrow smooth cylindrical passageway 43 adjacent the free end 44 thereof and expands into a threaded passageway 45 of greater diameter adjacent the hollow interior 39.

The cylinder heads 20 and 21 each have a radial bore respectively designated 46 and 47 extending through the cylinder head wall and communicating between the outside surface 23 and inside surface 24. The radial bores 46 and `47 are in the form of a narrow smooth cylindrical passageway 48 adjacent the inside surface 24 and expands into a threaded passageway 49 of greater diameter radially .outwardly of the narrow passageway 48.

A seal contacting shoulder 50 is formed in the respective cylinder heads and surrounds the radially extending bores 46 and 47 adjacent the respective outside surface 23. A seal receiving groove 51 surrounds the switch housing neck portion 36 adjacent the switch housing body portion 35 and an O-ring seal 52 is retained in the groove 51. The housing neck portion 36 is threadedly engaged in the threaded passageways 49 thereby mounting the switch housing 34 on the respective cylinder heads with the seal 52 being in hermetic sealing engagement between the end walls 38 and the shoulders 50.

A stern retainer 53, which may be of metal, is partially located within the switch housing interior 39 and has a threaded neck portion 54 'and an integral shank portion 55 and an integral central radial flange 56 therebetween. The neck portion 54 is threadedly engaged in the switch housing threaded passageway 45. The stem retainer 53 has an axial bore 57 therethrough and a pair of switch contact members 58 and 59 each have a washer-like body portion 68 with centering prongs 61 engaging sandwiching insulating washers 62 to maintain the switch contact members 58 and 59 out of electrical contact with each other and the stem retainer 53. The switch contact members 58 and 59 are locked in position on the stem retainer 53 by means of a bottom washer 63 which urges the body portions 60 of the switch contact members 58 and 59 and the sandwiching insulating washers 62 tightly against the integral radial flange 56 by virtue of an outwardly crimped ange 64 forming part of the stem retainer shank portion 55. The switch contact members 58 and 59 include respective resilient conductive contact arms 65 and 66 having free ends extending into spaced-apart relation in alignment with the axial bore 57. The contact arm 66 has, at the free end thereof, a contact button 67 normally spaced from the contact arm 65 but adapted to engage same as noted below. The switch Icontact members 58 and 59 also each have a terminal post, respectively designated 68 and 69, extending outwardly of the stem retainer 53 into the switch housing interior 39.

An elongated non-conductive switch stem 70 is slidably received in the stern retainer bore 57 and has an enlarged bulbous head 71 extending a measured distance into the respective cylinder head compartment 25 in the path of the respective piston end portions 32 and 33. The switch stem '70` has a stern portion 72 extending through the respective cylinder head bores 46 and 47, the switch housing bore 42 and the stem retainer bore 57 and ends in a tail portion 73 extending beyond the stem retainer 53 at the shank portion end 7 3. The tail portion 73 slidably engages the free end of the contact arm 65 for moving same against the button 67 when the switch stern 70 is axially moved downwardly is illustrated in FIG. 2.

The bores through which the switch stern extends are each of greater diameter than the corresponding portion of the switch stem whereby air is free to pass through the bores between the cylinder head compartment 25 and the respective switch housing interior 39. It is to be understood, however, that at least a portion of each of the bores are sufficiently close in inside diameter to the outside diameter of the corresponding part of the stem portion to provide accurate axial guidance for the switch stem and prevent undue bending even though the bulbous head 71 is contacted with a lateral as well as axial force by the piston end portions 32 and 33.

A snap ring groove 74 surrounds the switch stem adjacent the tail portion 73 and a snap ring 75 is engaged therein. The snap ring 75 interferes with the shank portion end of the stem retainer 53 thus preventing movement of the tail portion 73 into the stem retainer bore 57 although the portion 73 is continually resiliently urged in that direction by the contact arm 65. The proportions of the assembly are such that when the respective piston end portion 32 or 33 moves past the bulbous head 71 the switch stem is moved axially away from the piston end portion in a radial direction a distance suicient to cause the tail portion 73 to urge the contact arm 65 firmly into contact with the contact button 67. The stem movement does not stop at mere contact between the contact arm 65 and contact button 67 but continues causing the contact arm 65 to wipe or scrape against the contact button 67 so as to insure electrical continuity between the contact arms 65 and 66 while the respective piston end portions 32 or 33 covers the respective bulbous head 71.

A non-conductive sealing cap 76, preferably of the sarne material `as the switch housing 34, is in the shape of a disc with a protruding portion 77 having a diameter slightly smaller than the inside diameter of the switch housing whereupon it may be telescopically received thereinto at the open end 40. The sealing cap 76 has a greater diameter portion 78 adjacent the portion 77 and forming a radial flange 79 which contacts the open end portion of the side wall 37 to position the sealing cap 76. The sealing cap 76 is adhesively secured to the switch housing side wall 37 at the junction 80 therebetween whereby the switch housing 34 is closed and hermetically sealed at the open end 40.

The sealing cap 76 has a pair of spaced-apart wire feedthrough members 81 and 82 extending therethrough. Suitable conduit wires 83 and 84 are directed through the feedthrough members and are securely sealed therein by means of solder plugs 85. The conduit wires 83 and 84 are respectively electrically joined to the switch terminal posts 69 and 68. The feed-through members 81 and 82 each have an external terminal designated 86 and 87 for connecting electrical circuit conduits 88 and 89 thereto for electrical communication into the interior 39 of the respective signaling device while maintaining a seal against the atmosphere outside the cylinder assembly 1. A suitable cover member 90 is secured to the cylinder assembly 1 and covers the respective switch housings to protect same against physical contact which may cause damage.

In the illustrated embodiment of this invention the cylinder assembly is integrated into .an electrical circuit shown in FIG. l wherein the electrical conduit 89 branches and is common to one terminal each of the signaling device 18 and 19. The other terminal of the signaling device 19 is connected to a conduit 91. The cond-uits 88 and 89 are directe-d through control panel lights 92 and 93 to ground. The conduit 89 is directed through a suitable fuse or overload circuit breaker 94 into the main vehicle electrical system relay 95 which is connected in the usual manner through a cable 96 to the battery 97 normally carried in the vehicle. The relay 95 connects to an ignition switch 98 and controls current ow under appropriate conditions into the usual vehicle circuits by a network designated 99, such as, to the starting motor, ignition coil illumination circuits, etc.

The solenoid coil 100 of the solenoid valve control 4 has one conduit 101 directed through a safety switch 102 to ground. The other conduit 103 of the solenoid 100 is connected to one side of a relay switch 104 and the conduit 103 branches at 105 into contact with a conduit 1106 connected to one side of a relay coil 107 which operates the switch 104. The other side of the switch 104 is connected through a conduit 108 to the conduit 89 which is common to the signaling devices 18 and 19. The conduit 108 is also connected to one side of a normally open push butt-on switch 109. The other side of the switch 109 is connected through a conduit 1\10 to one side of a normally open switch 111 forming part of a multiple switch unit 112. The other side of the normally open switch 111 is connected to the conduit 106.

The other side of the relay coil 107 is connected through a conduit 1113 to one side of a normally closed switch 114 forming another portion of the switch unit 112, the other side of the normally closed switch 114 being connected to ground. The conduit 113 also communicates with one side of a normally closed push button switch 115 the other side of which connects to an additional normally closed push button switch 116 which is in series with ground potential.

In operation, when it is desired to engage the power take-off system, the safety switch 102 is closed and the engine of the vehicle is reduced to idling speed by a hand throttle control \117. This causes the normally open switch 111 to .close and the normally closed switch 114 to open. The push button switch 109 is then pushed closing same and causing current to tlow through the relay coil 107 and the normally closed switches 115 and 116 to ground which causes closure of the normally open relay switch 104. The relay switch 104 thereby locks itself in through a bridging current traveling through the conduit 105. The closure of the switch 104 actuates the solenoid valve 4 directing air into the forward portion 9 of the cylinder assembly 1. The operator observes that the piston 11 has started moving rearwardly by noting that the light 93 goes out, indicating that the piston is no longer in the forward-most position. Neither the light 92 nor 93 is lit during the time the piston 11 is traveling between the extreme positions of its stroke. When the rearward stroke is completed, the light 93 goes on indicating that the power take-olf is engaged.

Suitable variations in the circuit to the lights 92 and 93 may be made by those skilled in the art, for example, to show by an additional light (not shown) that the piston is in'an intermediate position. When the light 93 is lit the operator may increase the speed of the vehicle engine to operational condition which again closes the switch 114. This prevents accidental disengagement of a loaded power take-off by operating either of thenormally closed push button switches or \116. It is noted that the switches 115 and 116 perform the same function, that is, disengagement of the power take-olf under engine idling conditions, but may be located in remote locations for the convenience of the operator.

The operation of the signaling devices 18 and 19 is completely independent of the normal variations of pressure in the cylinder assembly 1 since such pressure variations are quickly equalized between the hollow interior 39 of the signaling devices and the cylinder compartments 25 associated respectively therewith. The hollow interiors 39 of the signaling devices are completely isolated from ambient or outside conditions and are exposed only to the normally clean and filtered air which enters the cylinder assembly 1. Any moisture which accidentally enters the cylinder assembly 1 and finds its way into the switch interiors is quickly flushed out with subsequent dry air during normal operation since there is a repeated in-rush and exhaust of air within the switch interiors. Any lubricant mist which finds its way into the posits on interior parts is not harmful since the contact button 67 is wiped across the free end of the contact arm 65 thus breaking through any existing insulating lubricant lm.

Itis to be understood that the use of the above described signaling devices is not limited to providing observed signals, but may be used, for example, to control the operation of solenoid valves to cause the piston in the assembly to continually reciprocate for a particular application. Therefore, this invention is not to be limited except insofar as such limitations are included in the following claims.

What I claim and desire to secure by Letters Patent is:

1. In combination with an air cylinder having a wall forming a closed piston chamber and a piston reciprocable in said chamber, i

(a) a switch assembly operating independently of variations of pressure in said piston chamber, said switch assembly having a housing forming an enclosed hollow interior, a bore in said housing providing the only access into said interior, a switch in said interior, a switch actuating member operably associated with said switch and movably extending through said bore and projecting outwardly of said housing, resilient means urging said switch actuating member outwardly of said housing,

(b) means mounting said housing on said chamber wall and providing a seal between said chamber wall and said housing, a passageway extending through said cylinder wall, said passageway being surrounded by said seal and communicating with said bore whereby the only communication into said interior is through said chamber,

(c) said actuating member movably extending through said passageway and into said chamber in the path of said piston, said actuating member being of lesser dimension than said bore and passageway whereby air is free to flow therepast into and out of said interior,

switch interior and de- (d) whereby said switch is actuated by contact between said piston and said actuating member independently of pressure variation in said cylinder.

2. The combination as set forth in claim 1 wherein:

(a) said switch assembly housing includes a body portion and a neck portion, said neck portion having said bore therethrough and external screw threads thereon, and

(b) said passageway has internal screw threads therein,

and

(c) said neck portion threads are threadedly engaged in said passageway threads for mounting said housing on said cylinder wall.

3. The combination as set forth in claim 2 wherein:

(a) said neck portion has a groove therearound, said means providing a seal including an O-ring seal in said groove,

(b) said sealing member being in sealing contract with said cylinder wall and said switch assembly body.

4. In combination:

(a) yan air cylinder having'a Wall forming a closed piston chamber, a reciprocal piston in said chamber, and

(b) a device for signaling that the piston has `achieved a predetermined position in said chamber, said device comprising:

(c) a switch housing including a body portion and a neck portion, said body portion having a side wall land one end Wall forming a hollow interior with an open end opposite to said one end wall, said neck portion protruding from said one end wall and having external screw threads thereon and a central bore extending axially therethrough and communicating through said one end wall with said hollow interior,

(d) said cylinder wall having a radial bore extending therethrough, screw threads in said cylinder wall bore, .said housing neck portion being threadedly engaged with said cylinder wall bore threads thereby mounting said switch housing on said cylinder wall, a seal in sealing engagement between said body portion end wall and said cylinder wall,

(e) a stern retainer in said -switch housing, said stem retainer having a bore therethrough and `a -pair of switch arms thereon and extending therebeyond in spaced apart relation in alignment with said stem retainer axial bore, said switch arms each having a terminal post communicating therewith and extending into said switch housing interior,

(f) an elongated switch stem slidably received in said stem retainer bore and having a bulbous head extending into said piston chamber in the path of said piston, said switch stem having a stem portion extending through said cylinder wall bore and said neck bore and said stem retainer bore and ending in a tail portion extending beyond said stern retainer, said tail portion slidably contacting said first switch arm, said bores each being of greater diameter than the corresponding portion of said switch stem whereby air is free to pass between said cylinder head compartment and said switch housing interior,

(g) a snap ring groove in said switch stern adjacent said tail portion, a snap ring in said last named groove to prevent movement of said tail portion into said stem retainer bore, said tail portion being adapted to urge said rst contact arm into sliding engagement with said second contact arm upon motion of said tail portion axially away from said stem retainer in response to sliding contact of said piston against said stem head, and

(h) a sealing cap adhesively secured to said switch housing, said sealing cap closing and sealing said switch housing open end, said sealing `cap having a pair of wire feedthrough members therein, a wire sealed in each of said feed-through members and joined respectively to said terminal posts, said feedthrough members each including an external terminal for connecting electrical conduits to said signaling device, whereby (i) said signaling device is sealed against ambient conditions and actuated directly by piston contact while being independent of variations in pressure in said air cylinder.

References Cited UNITED STATES PATENTS 2,499,958 3/1950 Knowlton 200-159 2,996,588 8/1951 Putnam 200-82 3,171,916 3/1965 Solski et al 200-82 BERNARD A. GILHEANY, Primary Examiner.

H. BROOME, Assistant Examiner, 

1. IN COMBINATION WITH AN AIR CYLINDER HAVING A WALL FORMING A CLOSED PISTON CHAMBER AND A PISTON RECIPROCABLE IN SAID CHAMBER, (A) A SWITCH ASSEMBLY OPERATING INDEPENDENTLY OF VARIATIONS OF PRESSURE IN SAID PISTON CHAMBER, SAID SWITCH ASSEMBLY HAVING A HOUSING FORMING AN ENCLOSED HOLLOW INTERIOR, A BORE IN SAID HOUSING PROVIDING THE ONLY ACCESS INTO SAID INTERIOR, A SWITCH IN SAID INTERIOR, A SWITCH ACTUATING MEMBER OPERABLY ASSOCIATED WITH SAID SWITCH AND MOVABLY EXTENDING THROUGH SAID BORE AND PROJECTING OUTWARDLY OF SAID HOUSING, RESILIENT MEANS URGING SAID SWITCH ACTUATING MEMBER OUTWARDLY OF SAID HOUSING, (B) MEANS MOUNTING SAID HOUSING ON SAID CHAMBER WALL AND PROVIDING A SEAL BETWEEN SAID CHAMBER WALL AND SAID HOUSING, A PASSAGEWAY EXTENDING THROUGH SAID CYLINDER WALL, SAID PASSAGEWAY BEING SURROUNDED BY SAID SEAL AND COMMUNICATION WITH SAID BORE WHEREBY THE ONLY COMMUNICATION INTO SAID INTERIOR IS THROUGH SAID CHAMBER, (C) SAID ACTUATING MEMBER MOVABLY EXTENDING THROUGH SAID PASSAGEWAY AND INTO SAID CHMBER IN THE PATH OF SAID PISTON, SAID ACTUATING MEMBER BEING OF LESSER DIMENSION THAN SAID BORE AND PASSAGEWAY WHEREBY AIR IS FREE TO FLOW THEREPAST INTO AND OUT OF SAID INTERIOR, (D) WHEREBY SAID SWITCH IS ACTUATED BY CONTACT BETWEEN SAID PISTON AND SAID ACTUATING MEMBER INDEPENDENTLY OF PRESSURE VARIATION IN SAID CYLINDER. 